Theorem pm5.501 242

Description: Theorem *5.501 of [WhiteheadRussell] p. 125. (Contributed by NM, 3-Jan-2005.) (Revised by NM, 24-Jan-2013.)

Assertion

Ref	Expression
pm5.501	⊢ (𝜑 → (𝜓 ↔ (𝜑 ↔ 𝜓)))

Proof of Theorem pm5.501

Step	Hyp	Ref	Expression
1		pm5.1im 171	. 2 ⊢ (𝜑 → (𝜓 → (𝜑 ↔ 𝜓)))
2		bi1 116	. . 3 ⊢ ((𝜑 ↔ 𝜓) → (𝜑 → 𝜓))
3	2	com12 30	. 2 ⊢ (𝜑 → ((𝜑 ↔ 𝜓) → 𝜓))
4	1, 3	impbid 127	1 ⊢ (𝜑 → (𝜓 ↔ (𝜑 ↔ 𝜓)))

Syntax hints:   → wi 4   ↔ wb 103

This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-ia1 104  ax-ia2 105  ax-ia3 106

This theorem depends on definitions:  df-bi 115

This theorem is referenced by:  ibib  243  ibibr  244  pm5.1  565  pm5.18dc  810  biassdc  1326